1. Field of the Invention
The present invention relates to an electrical connection box, such a junction block for an automotive vehicle, and in particular to a compact electrical connection box in which a fuse may be mounted. The present invention further relates to an electrical connection box designed to protect circuit boards during transportation, to reduce the number of parts and to reduce production cost.
2. Description of the Prior Art
A prior art large size electrical connection box, such as a junction block, includes internal circuits that are defined by a multitude of layers of busbars. Each layer is formed by pressing a conductive metal plate. Portions of the busbars are bent upwardly or downwardly in specified positions to form tabs to be connected with external circuits. The respective busbar layers are separated from one another by insulation plates.
If the internal circuits are constructed by busbars, production costs may increase because the shape of the busbars needs to be changed when the circuits are changed. In view of this problem, some internal circuits are constructed partially by busbars and partially by wires W and cramping terminals T connected with the wires W, (Japanese Unexamined Utility Model Publication No. 2-136989). Alternatively the internal circuits may be constructed only by wires and cramping terminals.
There are limits to downsizing electrical connection boxes. More specifically, if the minimum distance between adjacent tabs is shorter than 4 mm, a punch may not have sufficient strength to form the conductive metal plate. In particular, the punch may be broken or the formed busbars may not have accurate dimensions. As a result the minimum distance between adjacent tabs formed in busbars typically is 4 mm. These dimensions prevent busbars from being used with closely spaced connectors or with compact integrated fuse having fusible elements arranged at intervals smaller than the spacing of the busbars. Accordingly, it is necessary to use larger connectors and larger fuses with busbars, thereby making the prior art electrical connection box large.
If the internal circuits are constructed by wires and cramping terminals, the intervals between connectors or fuses typically is determined by the size of the cramping portions. Thus, miniaturization necessitates smaller cramping terminals or thinner wires. However, smaller prior art cramping terminals cannot generate a sufficient connection force. On the other hand, thinner wires elongate during manufacturing, thereby causing a problem during assembling.
To respond to an increase of signal circuits as the internal circuits in recent years, the applicant of the present invention proposed a flat fuse 3 in which fusible elements 2 made of a metal wire or a metal foil tape are arranged in parallel and are adhered to both front and rear surfaces of an insulation plate 1 at specified intervals as shown in FIGS. 6(A) and 6(B) of this application and in Japanese Patent Applications Nos. 7-91698 and 7-91699. FIGS. 6(A) and 6(B) also show a fuse cover 5, an upper casing 6 of the electrical connection box, and a fuse fitting portion 6a provided at the upper casing. If this flat fuse 3 is used, circuits cannot be connected with the fusible elements 2A, 2B, . . . in one-to-one relationship without enlarging an installation space.
This prior art compact fuse creates busbar manufacturing difficulties. Specifically, the busbar is formed by pressing a conductive metal plate. Portions of the busbar are bent upright to form tabs. These tabs need to be connected with the terminals of the fuse. At this time, it is necessary to form the narrowly spaced parallel tabs to conform to the narrowly spaced parallel fusible elements of the flat fuse. However, as noted above, it is difficult to form busbars having such tabs because of a limit in punching strength tolerated by a press used to form the busbars. In other words, the use of a conventional busbar as the internal circuits of the electrical connection box is not compatible with the compact integrated fuse.
The above problem can be solved if the busbar can be connected with the compact integrated fuse by forming tabs to be connected with adjacent fusible elements not in the same busbars, but in busbars at different layers. However, in such a case, the number of busbar layers increases, leading to an increased production cost, making the electrical connection box larger and complicated, and eliminating a degree of freedom in circuit designing for the busbar.
Furthermore in a prior art circuit protection system for an automotive wiring harness, a fuse is provided between a power source and a load so that, upon a flow of an overcurrent, it blows out to protect the circuitry. Fuses used in the prior art devices include blade fuses and mini fuses. These fuses have a single electrode and, therefore, can be connected with only a single circuit.
It is often desirable to connect essential circuits to fuses in one-to-one relationship. It also is sufficient that the current carrying capacity of the fuses be below 5 ampere (A). However, as shown in FIG. 12, a plurality of circuits C1 to C3, at present, are collected into one circuit C4 which is connected with one fuse H of 5 A or larger. About 70% of the circuits connected with the fuses are signal circuits connected with loads having a current carrying capacity of 1 A or smaller. Even in this case, a plurality of signal circuits also are collected and connected with a fuse having a current carrying capacity of 5 A or larger.
However, in the case that a plurality of circuits are collected and connected with one fuse as described above, even if the fuse blows out when a problem occurs in a circuit which is not particularly important, essential circuits connected with the same fuse are affected. This problem can be avoided by connecting the essential circuits with the fuses in one-to-one relationship, but this leads to an increase in the number of fuses to be installed. Especially when prior art blade fuses are adopted, a space for installing these fuses considerably increases, thereby making the electrical connection box larger.
However, if a conventionally used busbar is adopted as circuits of the electrical connection box to be connected with the flat fuse, it is difficult to provide connection terminals to be connected with the respective fusible elements of the flat fuse.
As shown in FIG. 16, electrical connection boxes 201 of the above type have conventionally been shipped to a car manufacturer while electronic units 203 are accommodated in electronic unit containers 202 separate from the electrical connection boxes 201 in order to prevent circuit boards 204 carrying the electronic units 203 from being damaged during transportation to the car manufacturer. At an assembly line of automotive vehicles, the containers 202 housing the electronic units 203 corresponding to the grades of the vehicles are fittably connected with container mount portions 201a of the electrical connection boxes 201.
The above electronic unit container 202 is comprised of lower and upper casings 205, 206 which can be lockingly fitted with each other. The electronic unit container 202 is mounted on the electrical connection box 201 by engaging a locking portion 206a formed on the outer surface of the upper casing 206 with an engaging portion (not shown) of the electrical connection box 201. Further, an opening 206b for exposing a fitting portion 207a of a connector 207 connected with the circuit board 204 is formed in the upper surface of the upper casing 206 so as to allow the connection of the connector 207 with a connector portion 201b of the electrical connection box 201.
The electrical connection box 201 needs the separate electronic unit container 202, which increases the number of parts. Accordingly, there is a problem of a high production cost. Further, since two parts: the electrical connection box 201 and the electronic unit container 202 have to be shipped to the car manufacturer, there is a problem of a higher transportation cost.
Furthermore, at the assembly line, when the container 202 is fittably connected with the electrical connection box 201, an electrical connection check for checking whether or not the box 201 and the container 202 are securely connected cannot be made. Accordingly, when the container 202 is improperly connected with the electrical connection box 201, the electrical connection box 201 cannot properly function.
The present invention was developed in view of the above problems, and an object thereof is to downsize a large electrical connection box such as a junction block by forming conductive members of internal circuits of the electrical connection box in conformity with amounts of current to flow in the circuits and arranging the conductive members at small intervals so as to be connected with external terminals.
It is another object of the present invention is to provide an electrical connection box with internal circuits easily connectable with parallel narrowly arranged fusible elements of a compact integrated fuse.